Catalyst for reducing carbon monoxide concentration

Abstract

Disclosed in a catalyst which enables to reduce the carbon monoxide concentration in a product gas to 5 ppm by volume or less when carbon monoxide in a raw material gas containing hydrogen and carbon monoxide is selectively oxidized. The catalyst comprises a support of an inorganic oxide and ruthenium loaded thereon, and the relative loading depth X(Ru) of ruthenium in the radial direction in a redial cross-section of the catalyst satisfies the requirement defined by the following formula (1) X(Ru)≧15  (1).

1. A catalyst used in a method for reducing the carbon monoxide concentration of a raw material gas containing hydrogen and carbon monoxide by bringing the raw material gas into contact with an oxygen-containing gas in the presence of the catalyst to selectively oxidize carbon monoxide in the raw material gas, comprising a support of an inorganic oxide and ruthenium loaded thereon, the relative loading depth of ruthenium X(Ru) in the radial direction of the catalyst in a radial cross-section of the catalyst satisfying the requirement represented by the following formula (1):
   X(Ru)≧15  (1)
 
 
       wherein the relative depth of ruthenium X(Ru) indicates the ratio (%) of the loading depth of ruthenium to the radius of the catalyst particle, wherein in addition to ruthenium, the catalyst further comprises at least one metal selected from the group consisting of platinum, palladium, rhodium and iridium. 
     
     
       2. The catalyst according to  claim 1 , wherein when the cross-section thereof cut through a plane along the radial direction is line-analyzed using EPMA to determine the concentration level Y 1  at the position where the ruthenium concentration is maximum, the position P 1  where the ruthenium concentration is 5 percent of Y 1 , the outermost surface of the catalyst P 0 , and the midpoint Pm between P 0  and P 1 , the maximum ruthenium concentration level Y 2  in the area between Pm and P 1  and Y 1  satisfy the requirement defined by the following formula:
   1.1≦ Y 1/ Y 2≦10  (3).
 
 
     
     
       3. A method for reducing carbon monoxide concentration comprising:
 bringing a raw material gas containing hydrogen and carbon monoxide into contact with an oxygen-containing gas in the presence of the catalyst according to  claim 2  to reduce the carbon monoxide concentration in the raw material gas to 3.5 ppm by volume or less. 
 
     
     
       4. The catalyst according to  claim 1 , wherein the inorganic oxide is at least one type selected from the group consisting of aluminum oxide, silicon oxide, zirconium oxide and titanium oxide. 
     
     
       5. A method for reducing carbon monoxide concentration comprising:
 bringing a raw material gas containing hydrogen and carbon monoxide into contact with an oxygen-containing gas in the presence of the catalyst according to  claim 1  to reduce the carbon monoxide concentration in the raw material gas to 5 ppm by volume or less. 
 
     
     
       6. An apparatus for producing a hydrogen-rich gas by reducing the carbon monoxide concentration in the raw material gas using the methods according to  claim 5 . 
     
     
       7. A fuel cell system comprising a cathode, wherein the hydrogen-rich gas produced with the apparatus according to  claim 6  is supplied as a fuel for the cathode.